Generally, in chemotherapy of tumor, particularly malignant tumor, an exclusive administration of an antitumor agent rarely results in a desired antitumor effect. To enhance the effect, a multiple drug therapy using, in combination, 2, 3 or more drugs having different action mechanisms, has been employed in clinical situations. In this combination therapy, antitumor agents having different action mechanisms are combined 1) to decrease insensitive cell population, 2) to prevent or delay appearance of drug-resistance, 3) to disperse toxicity by the combination of pharmaceutical agents having different toxicities, and the like, thereby decreasing side effects and enhancing antitumor action. However, aimless combination of antitumor agents having different action mechanisms for combination therapy does not necessarily lead to an enhanced antitumor effect, and therefore, a combination effect afforded by the combination of antitumor agents exhibiting higher antitumor activities has been studied.
It has been reported that a compound represented by the formula (I)
and a pharmaceutically acceptable salt thereof (hereinafter to be also referred to as compound A; SEQ ID; No 1), and particularly a stereoisomer of the formula (II)
(hereinafter to be also referred to as FK228) and a pharmaceutically acceptable salt thereof strongly and selectively inhibit histone deacetylase to derive a potent antitumor activity, and that the substances cause high acetylation of histone in the treated cells, thereby inducing transcription-regulatory activity of various genes, cell cycle inhibitory activity and apoptosis (e.g., JP-B-7-64872, “Experimental Cell Research”, US (1998), vol. 241, pp. 126-133).
However, there is no report as yet on the combined use of a histone deacetylase inhibitor such as Compound A and the like, and a topoisomerase II inhibitor, and the effect afforded by the combined use.
Histone deacetylase is a metallo-deacetylating enzyme coordinating Zn at an active center (M. S. Finnin et al., Nature, 401, 188-193 (1999)). This enzyme is considered to change affinity of various acetylated histones for DNA. The direct biological phenomenon brought thereby is a change in the chromatin structure. The minimum unit of the chromatin structure is a nucleosome wherein 146 bp DNA is wound 1.8 times anticlockwise around a histone octamer (H2A, H2B, H3 and H4, each 2 molecules, core histone). The core histone stabilizes the nucleosome structure by interaction of the positive charge of the N-terminus of each histone protein with DNA. Acetylation of histone is controlled by the equilibrium between an acetylation reaction involving histone acetyltransferase and a deacetylation reaction involving histone deacetylase. It is considered that the histone acetylation occurs at a lysine residue where the histone protein N-terminal is evolutionally preserved well, due to which a core histone protein loses charges at the N-terminal, interaction with DNA is attenuated, and the structure of nucleosome becomes unstable. Accordingly, the histone deacetylation is considered to be the reverse thereof, namely, a shift toward stabilization of the nucleosome structure. However, to what degree the acetylation changes the chromatin structure and how it relates to the transcriptional regulation etc. secondarily induced thereby are unclear in many aspects.
An object of the present invention is to provide an antitumor agent causing reduced side-effects and a superior antitumor activity based on the combined use of a topoisomerase II inhibitor as an antitumor agent, and a pharmaceutical agent that strikingly enhances an antitumor effect of the inhibitor.